Sensor

ABSTRACT

A sensor includes a cylindrical housing having an apertured planar base wall and contact plate. An axial pole magnet is mounted on the base wall and located normal to the aperture. The magnetic flux of the magnet maintains a ball in seated relationship within a ball seat provided by the embossed opening of the apertured plate. The OD of the ball is greater than that of the magnet. A contact ring is mounted on a circular sidewall of the housing and includes a peripheral series of integral cantilevered thin flexible axially tapered spring fingers which extend radially of the ball seat and overlie the contact plate in spaced relationship. The distal portions of the fingers terminate radially outwardly of the ball seat and are spaced from the contact plate a distance greater than the OD of the ball. An intermediate portion of each finger is spaced from the contact plate a distance substantially equal to the OD of the ball. The contact plate and the contact ring are connected to a source of power and a mechanism to be actuated. Upon an acceleration pulse of predetermined amplitude and time being applied to the ball, the ball moves radially outwardly of the ball seat and into wiping engagement with the contact plate and at least one of the spring fingers to complete the circuit across the source of power and the mechanism to be actuated. The wiping engagement of the ball with the intermediate portion of the one finger flexes the one finger about its proximal portion and creates a spring biasing force returning the ball toward the ball seat when the acceleration pulse is reduced. A cover for the housing seats on the sidewall and includes a stop projecting transverse of the distal portion of the fingers and overlying the ball seat to limit movement of the ball axially of the seat.

Attorneys-W. E. Finken and Herbert Furman United States Patent [72]lnventor ArdenG.Gillund OakCreek,Wis. [21] AppLNo. 35,674 [22] FiledMays, 1970 [45] Patented Nov. 9, 1971 [73] Assignee GeneralMotorsCorporation Detr0it,Mich.

[54] SENSOR 4 Claims, 3 Drawing Figs.

[52] U.S.Cl zoo 61.45, 200/52, 340/262 [51] Int-Cl ..H01h35/02 [50]FieldofSearch 340/262; 200/61.45,61.46,61.47,61.48,61.49,61.51,6l.52,6l.53,52, 166.1, 166 F, 163

[56] References Cited UNITED STATES PATENTS 2,997,557 8/1961 GillmoretalZOO/61.45 2,890,303 6/1959 Clurman.... ZOO/61.45 2,892,049 6/1959Rubinstein ZOO/61.45 2,898,415 8/1959 Clurman.... ZOO/61.53 2,888,5305/1959 Horton ZOO/61.45

Primary Examiner-J. V. Truhe Assistant Examiner-George A. MontanyeABSTRACT: A sensor includes a cylindrical housing having an aperturedplanar base wall and contact plate. An axial pole magnet is mounted onthe base wall and located normal to the aperture. The magnetic flux ofthe magnet maintains a ball in seated relationship within a ball seatprovided by the embossed opening of the apertured plate. The OD of theball is greater than that of the magnet. A contact ring is mounted on acircular sidewall of the housing and includes a peripheral se- 7 ries ofintegral cantilevered thin flexible axially tapered spring fingers whichextend radially of the ball seat and overlie the contact plate in spacedrelationship. The distal portions of the fingers terminate radiallyoutwardly of the ball seat and are spaced from the contact plate adistance greater than the OD of the ball. An intermediate portion ofeach finger is spaced from the contact plate a distance substantiallyequal to the OD of the ball. The contact plate and the contact ring areconnected to a source of power and a mechanism to be actuated. Upon anacceleration pulse of predetermined amplitude and time being applied tothe ball, the ball moves radially outwardly of the ball seat and intowiping engagement with the contact plate and at least one of the springfingers to complete the circuit across the source of power and themechanism to be actuated. The wiping engagement of the ball with theintermediate portion of the one finger flexes the one finger about itsproximal portion and creates a spring biasing force retuming the balltoward the ball seat when the acceleration pulse is reduced. A cover forthe housing seats on the sidewall and includes a stop projectingtransverse of the distal portion of the fingers and overlying the ballseat to limit movement of the ball axially of the seat.

SENSOR This invention relates to sensors and more particularly tosensors of the type including a ball retained in a predeterminedposition by magnetic flux and being movable to a position completing anelectrical circuit when subjected to an acceleration pulse ofpredetermined amplitude and time.

One of the features of the sensor of this invention is that the ball isretained within a ball seat on a planar surface by magnetic flux and ismovable radially of the ball seat when subjected to an accelerationpulse of predetermined amplitude and time into wiping engagement with anintermediate portion of at least one of a plurality of axially taperedcantilevered spring fingers and a conductive area on the planar surfaceto close a circuit between the one spring finger and conductive area andactuate a mechanism. Another feature of this invention is that thewipingly engaged spring finger flexes about its proximal portion whenwipingly engaged by the ball to create a biasing force returning theball toward the ball seat upon reduction or cessation of theacceleration pulse. A further feature of this invention is that thewiping engagement of the ball with the spring fingers and the conductivearea of the planar surface continuously maintains a clean surface forexcellent electrical contact. Yet another feature of this invention isthat a stop limits movement of the ball axially of the ball seat. Yet afurther feature of this invention is that the spring fingers are locatedgenerally radially of the ball seat and the intermediate portions of thefingers may be at the same distance or different distances from the ballseat to thereby provide equal or varying integrated distances for theball. These and other features of the sensor of this invention will bereadily apparent from the following specification and drawings wherein:

FIG. 1 is a partially broken away top plan view of a sensor according tothis invention in unactuated position;

FIG. 2 is an enlarged cross-sectional view taken generally along theplane indicated by line 2-2 of FIG. 1; and

FIG. 3 is a view similar to FIG. 2 showing the sensor in actuatedposition.

Referring now to FlGs. l and 2 of the drawings, a sensor according tothis invention includes a closed housing designated generally 12. Thehousing 12 includes a circular base member 14 of plastic or otherinsulating material having a central bore 16 which opens through asmaller diameter bore 18 to the upper planar wall or surface 20 of themember 14. An axial pole magnet 22 fits within the bore 16 and issuitably secured therein as by cementing. In the specific embodimentshown, the north pole of the magnet is located adjacent the aperture 18although the poles of the magnet can be reversed if desired.

A circular contact plate 24 of electrically conductive material seats onthe wall 20 and includes a central opening having an embossed edgeopening to the aperture 18 and providing a ball seat 26. A ball 28 ofmagnetic electrically conductive material is seated on the seat 26. TheOD of the ball is greater than that of the magnet 22. The magnetic fluxof the magnet 22 normally holds the ball on seat 26 against movementalong the upper planar wall or surface 30 of plate 24.

A circular spacer ring 32 of insulating material seats on the edgeportion of plate 24. A circular contact ring 34 seats on the upper wallof the ring 32. A circumferential series of like adjacent spaced axiallytapered spring fingers 36 extend generally radially of the ring and ofthe ball seat 26. The proximal portions of the spring fingers areintegrally joined to ring 34 at 38 and cantilever the fingers inoverlying angularly spaced relationship to surface 30. Preferably theangle between each finger and the surface 28 is at leastlO". The freeends or distal portions of the fingers 36 terminate radially outwardlyof the ball seat 26 and are spaced from the surface 30 a distancegreater than the OD of the ball 28. An intermediate portion 40 of eachfinger is spaced from the surface 30 a distance generally equal to theOD of the ball 28. Preferably the ring 34 and fingers 36 are formed ofvery thin flexible electrically conductive material, such as berylliumcopper or harddrawn brass.

A circular cover 42 for the housing 10 is formed of insulating materialand includes an outer peripheral flange or wall 44 which seats on thering 34 and a central annular embossment or stop 46 which axiallyoverlies the ball seat 26 and is located immediately adjacent the ball28 for a purpose to be described. Rivets 48 extend through alignedapertures in the wall 44 of cover 42, ring 34, spacer 32, plate 24 andbase 14 to maintain the sensor parts in assembled relationship. Theplate 24 and the ring 34 include respective contact terminals 50 and 52.As shown, terminal 52 is grounded and terminal 50 is connected to abattery or other source of power and a mechanism M to be actuated by thesensor.

Under acceleration impulses of predetermined amplitude and time appliedgenerally coaxial of the sensor, or normal to surface 30, the ball 28may move axially of the seat 26 against the flux of magnet 22, but willimmediately engage the embossment 46 to stop such movement of the balland immediately return it in seated relationship on the ball seat 26.

When an acceleration pulse of predetermined amplitude and time isapplied generally normal to the axis of the sensor, or horizontally asviewed in FIG. 2, the ball 28 will move radially of the ball seat 26 andalong the surface 30 against the flux of magnet 22. The ball will freelymove underneath the distal portion of at least one of the fingers 36 andthen move into wiping engagement with the intermediate portion 40 of theone finger and with the surface 30 as shown in FIG. 3. This completesthe circuit and actuates the mechanism M controlled by the sensor 10.

The wiping engagement of the ball 28 with the one finger 36 flexes theone finger about the proximal portion thereof as shown in FIG. 3. Eachfinger functions as an individual tapered leaf spring member and flexingof any one of the fingers by the ball causes the finger to apply aresilient biasing force on the ball which is directed generally radiallyof the ball seat 26 and returns the ball along surface 30 toward theball seat when the acceleration pulse is reduced or ceases. As soon asthe ball moves toward the ball seat and out of engagement with theflexed finger, the finger will return to its normal position shown inFIG. 2.

The resilient biasing force or output of the engaged finger must besufficient to return the ball 28 a predetermined distance toward theball seat 26 so that the magnetic flux of the magnet 22 can reseat theball.

It is important that the ball 28 wipingly engage the spring fingers 36to flex such fingers about the proximal portions thereof and yet notwedge between the fingers and the surface 30. While the foregoingdescription describes the operation of the sensor in terms of engagementof the ball 28 with one of the fingers, it is believed clear that theball could wipingly engage at least two of the fingers. In such instancethe surface of the ball would engage adjacent juxtaposed edges of two ofthe fingers.

The angle at which the spring fingers 36 extend with respect to thesurface 30 will vary with other dimensions of the sensor, such as thespherical diameter of ball 28. It is also important that the ball 28 beof magnetic material but not be a magnet itself.

Although the axially tapered fingers 36 are shown as being arranged in acircular pattern, it is believed clear that they can be arranged inother patterns such as oval, elliptical or irregular. A noncircularpattern of arrangement would provide varying integrated distancesbetween the ball seat and the intermediate portion of certain or all ofthe spring fingers so that the responsive time of the sensor will varywith the direction of impulse. The integrating distance is the radialdistance between the ball seat and the point of tangential engagement ofthe ball 28 with the surface 30 at the time that the ball 28 initiallywipingly engages any one of the fingers.

Likewise, although the plate 24 is shown as being continu ous, it isbelieved apparent that the plate could be segmented and extendunderneath the intermediate portions of only certain of the springfingers to thereby complete the circuit across the sensor 10 only whenthe acceleration pulses are received in certain directions. Likewise,plate 24 could be omitted and the upper wall 20 of the member 14 couldbe provided with a printed circuit, either continuous or segmented, toprovide for either an omnidirectional sensor or a sensor which willcomplete the circuit only when the acceleration pulse is received incertain directions.

In the specific embodiment shown, one ball 28 is provided. However, aplurality of balls, preferably three, could be used. Three balls wouldrequire a ball seat of larger diameter such that the balls would betangent to each other within the seat as well as tangentially engage theedge of the seat. In a sensor having a multiplicity of balls, the ballswould tend to cancel any resonance by engagement with each other shouldthe acceleration pulses be below the predetermined threshold value ortime.

The sensor of this invention is particularly intended for use in an aircushion restraint system for a vehicle. In such a system, adiaphragm-sealed pressure vessel communicates with a manifold which inturn communicates with a cushion or bag intended to be inflated when thevehicle is subjected to certain acceleration pulses. The diaphragm ofthe pressure vessel is ruptured by one or more squibs which areelectrically fired. The sensor 10 could be connected in series with suchsquibs and a source of power to fire the squibs and release the pressurefluid to inflate the cushion when the ball of the sensor and, of course,the vehicle are subjected to acceleration pulses which exceedpredetermined threshold values of both amplitude and time.

Thus, this invention provides an improved sensor.

l claim:

l. A sensor comprising, in combination, a housing including a planarwall, means providing a ball seat on the planar wall, an axial polemagnet located generally normal to the planar wall and communicatingwith the ball seat, a ball of magnetic electrically conductive materialseated on the ball seat, the flux of the magnet holding the ball againstmovement radially of the ball seat along the planar wall, a series ofadjacent flexible spring fingers of electrically conductive materialspaced generally laterally of the planar wall and having their proximalportions supported on the housing, the fingers extending generallyradially of the ball seat and at predetermined angles to the planarwall, the distal portions of the fingers terminating radially outwardlyof the ball seat and being spaced from the planar wall a distancegreater than the OD of the ball, an intermediate portion of each fingerbeing spaced from the planar wall a distance generally equal to the ODof the ball, means on the planar wall providing an electricallyconductive area under the intermediate portion of each finger, theconductive area under the intermediate portion of each finger, theconductive area and the fingers being adapted to connect a source ofpower to a mechanism to be actuated by the sensor, an acceleration pulseof predetermined amplitude and time overcoming the flux of the magnetand moving the ball radially of the ball seat along the planar wall, theball moving underneath the distal portion of at least one finger andinto wiping engagement with the conductive area and the intermediateportion of the one finger to connect the source of power to themechanism to be actuated and to flex the one finger about the proximalportion thereof, the flexing of the one finger providing a resilientbiasing force on the ball directed generally radially of the ball seatand returning the ball along the planar wall toward the ball seat uponreduction of the acceleration pulse.

2. A sensor comprising, in combination, a housing including a planarwall having an aperture therethrough, means providing a ball seat on theplanar wall adjacent the aperture, an axial pole magnet locatedgenerally normal to the planar wall of the housing and communicatingwith the ball seat through the aperture, a ball of magnetic electricallyconductive material seated on the ball seat, the flux of the magnetholding the ball against movement radially of the ball seat along theplanar wall, a series of adjacent flexible spring fingers ofelectrically conductive material spaced laterally of the planar wall andhaving their proximal portions supported on the housing, the

fingers extending generally radially of the ball seat and atpredetermined angles to the planar wall, the distal portions of thefingers terminating radially outwardly of the ball seat and being spacedfrom the planar wall a distance greater than the OD of the ball, anintermediate portion of each finger being spaced from the planar wall adistance generally equal to the OD of the ball, means on the planar wallproviding an electrically conductive area under the intermediate portionof each finger, the conductive area and the fingers being adapted toconnect a source of power and a mechanism to be actuated by the sensor,an acceleration pulse of predetermined amplitude and time overcoming theflux of the magnet and moving the ball radially of the ball seat alongthe planar wall, the ball moving underneath the distal portion of atleast one finger and into wiping engagement with the conductive area andthe intermediate portion of the one finger to connect the source ofpower to the mechanism to be actuated and to flex the one finger aboutthe proximal portion thereof, the flexing of the one finger providing aresilient biasing force on the ball directed generally radially of theball seat and returning the ball along the planar wall toward the ballseat upon reduction of the acceleration pulse, and means on the housingoverlying the ball seat and limiting movement of the ball axially of theseat.

3. A sensor comprising, in combination, a housing having an annularsidewall and a planar base wall having an aperture therethrough, meansproviding a ball seat on the planar wall adjacent the aperture, an axialpole magnet located generally normal to the planar wall of the housingand communicating with the ball seat through the aperture, a ball ofmagnetic electrically conductive material seated on the ball seat, theflux of the magnet holding the ball against movement radially of theball seat along the planar wall, an annular series of adjacent flexiblespring fingers of electrically conductive material peripherallysurrounding the ball seat, means mounting the proximal portions of thefingers on the sidewall of the housing to cantilever the fingers overthe planar wall at predetermined angles thereto, the distal portions ofthe fingers being spaced from the planar wall a distance greater thanthe OD of the ball, an intermediate portion of each finger being spacedfrom the planar wall a distance generally equal to the OD of the ball,means on the planar wall providing an electrically conductive area underthe intermediate portion of each finger, the conductive area and thefingers being adapted to connect a source of power and a mechanism to beactuated by the sensor, an acceleration pulse of predetermined amplitudeand time overcoming the flux of the magnet and moving the ball radiallyof the ball seat along the planar wall, the ball moving underneath thedistal portion of at least one finger and into wiping engagement withthe conductive area and the intermediate portion of the one finger toconnect the source of power and the mechanism to be actuated and to flexthe one finger about the proximal portion thereof, the flexing of theone finger providing a resilient biasing force on the ball directedgenerally radially of the ball seat and returning the ball along theplanar wall toward the ball seat upon reduction of the accelerationpulse.

4. A sensor comprising, in combination, a housing including an aperturedannular base wall having a planar surface, an annular sidewall extendinglaterally of the base wall and an annular end wall spaced laterally ofthe base wall, means providing a ball seat on the base wall adjacent theaperture, an axial pole magnet located generally normal to the planarsurface of the housing and communicating with the ball seat through theaperture, a ball of magnetic electrically conductive material seated onthe ball seat, the flux of the magnet holding the ball against movementradially of the ball seat along the planar surface, an annular series offlexible spring fingers of electrically conductive material cantileveredon the sidewall and overlying the planar surface, the fingers extendinggenerally radially of the ball seat and at predetermined angles to theplanar surface, the distal portions of the fingers terminating radiallyoutwardly of the ball seat and being spaced from the planar surface adistance greater than the OD of the ball, an intermediate portion ofeach finger being spaced from the planar surface a distance generallyequal to the OD of the ball, means on the planar surface providing anelectrically conductive area under the intermediate portion of eachfinger, the conductive area and the fingers being adapted to connect asource of power and a mechanism to be actuated by the sensor, anacceleration pulse of predetermined amplitude and time overcoming theflux of the magnet and moving the ball radially of the ball seat alongthe planar surface, the ball moving underneath the distal portion of atleast one finger and into wiping engagement with the conductive area andthe intermediate portion of the one finger to connect the source ofpower and the mechanism to be actuated and to flex the one finger aboutthe proximal portion thereof, the flexing of the one finger providing aresilient biasing force on the ball directed generally radially of theball seat and returning the ball along the planar surface toward theball seat upon reduction of the acceleration impulse, and means on theend wall projecting between the distal portions of the fingers andoverlying the ball seat to limit movement of the ball laterally of theball seat.

i i t i k Patent No.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,619,524 DatedNovember 9, 1971 lnvencorks) Arden G. Gillund It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Column 3, lines 50 and 51, the following language should be deleted: theconductive area under the intermediate portion of each finger,

line 53, "to" (first occurrence) should read and Signed and sealed this13th day of June T972.

(SEAL) Attest:

R0 BERT GOI'ISCHALK EDWARD M.FLETCI-ER,JR.

Commissioner of Patents Attesting Officer

1. A sensor comprising, in combination, a housing including a planarwall, means providing a ball seat on the planar wall, an axial polemagnet located generally normal to the planar wall and communicatingwith the ball seat, a ball of magnetic electrically conductive materialseated on the ball seat, the flux of the magnet holding the ball againstmovement radially of the ball seat along the planar wall, a series ofadjacent flexible spring fingers of electrically conductive materialspaced generally laterally of the planar wall and having their proximalportions supported on the housing, the fingers extending generallyradially of the ball seat and at predetermined angles to the planarwall, the distal portions of the fingers terminating radially outwardlyof the ball seat and being spaced from the planar wall a distancegreater than the OD of the ball, an intermediate portion of each fingerbeing spaced from the planar wall a distance generally equal to the ODof the ball, means on the planar wall providing an electricallyconductive area under the intermediate portion of each finger, theconductive area and the fingers being adapted to connect a source ofpower to a mechanism to be actuated by the sensor, an acceleration pulseof predetermined amplitude and time overcoming the flux of the magnetand moving the ball radially of the ball seat along the planar wall, theball moving underneath the distal portion of at least one finger andinto wiping engagement with the conductive area and the intermediateportion of the one finger to connect the source of power to themechanism to be actuated and to flex the one finger about the proximalportion thereof, the flexing of the one finger providing a resilientbiasing force on the ball directed generally radially of the ball seatand returning the ball along the planar wall toward the ball seat uponreduction of the acceleration pulse.
 2. A sensor comprising, incombination, a housing including a planar wall having an aperturetherethrough, means providing a ball seat on the planar wall adjacentthe aperture, an axial pole magnet located generally normal to theplanar wall of the housing and communicating with the ball seat throughthe aperture, a ball of magnetic electrically conductive material seatedon the ball seat, the flux of the magnet holding the ball againstmovement radially of the ball seat along the planar wall, a series ofadjacent flexible spring fingers of electrically conductive materialspaced laterally of the planar wall and having their proximal portionssupported on the housing, the fingers extending generally radially ofthe ball seat and at predetermined angles to the planar wall, the distalportions of the fingers terminating radially outwardly of the ball seatand being spaced from the planar wall a distance greater than the OD ofthe ball, an intermediate portion of each finger being spaced from theplanar wall a distance generally equal to the OD of the ball, means onthe planar wall providing an electrically conductive area under theintermediate portion of each finger, the conductive area and the fingersbeing adapted to connect a source of power and a mechanism to beactuated by the sensor, an acceleration pulse of predetermined amplitudeand time overcoming the flux of the magnet and moving the ball radiallyof the ball seat along the planar wall, thE ball moving underneath thedistal portion of at least one finger and into wiping engagement withthe conductive area and the intermediate portion of the one finger toconnect the source of power to the mechanism to be actuated and to flexthe one finger about the proximal portion thereof, the flexing of theone finger providing a resilient biasing force on the ball directedgenerally radially of the ball seat and returning the ball along theplanar wall toward the ball seat upon reduction of the accelerationpulse, and means on the housing overlying the ball seat and limitingmovement of the ball axially of the seat.
 3. A sensor comprising, incombination, a housing having an annular sidewall and a planar base wallhaving an aperture therethrough, means providing a ball seat on theplanar wall adjacent the aperture, an axial pole magnet locatedgenerally normal to the planar wall of the housing and communicatingwith the ball seat through the aperture, a ball of magnetic electricallyconductive material seated on the ball seat, the flux of the magnetholding the ball against movement radially of the ball seat along theplanar wall, an annular series of adjacent flexible spring fingers ofelectrically conductive material peripherally surrounding the ball seat,means mounting the proximal portions of the fingers on the sidewall ofthe housing to cantilever the fingers over the planar wall atpredetermined angles thereto, the distal portions of the fingers beingspaced from the planar wall a distance greater than the OD of the ball,an intermediate portion of each finger being spaced from the planar walla distance generally equal to the OD of the ball, means on the planarwall providing an electrically conductive area under the intermediateportion of each finger, the conductive area and the fingers beingadapted to connect a source of power and a mechanism to be actuated bythe sensor, an acceleration pulse of predetermined amplitude and timeovercoming the flux of the magnet and moving the ball radially of theball seat along the planar wall, the ball moving underneath the distalportion of at least one finger and into wiping engagement with theconductive area and the intermediate portion of the one finger toconnect the source of power and the mechanism to be actuated and to flexthe one finger about the proximal portion thereof, the flexing of theone finger providing a resilient biasing force on the ball directedgenerally radially of the ball seat and returning the ball along theplanar wall toward the ball seat upon reduction of the accelerationpulse.
 4. A sensor comprising, in combination, a housing including anapertured annular base wall having a planar surface, an annular sidewallextending laterally of the base wall and an annular end wall spacedlaterally of the base wall, means providing a ball seat on the base walladjacent the aperture, an axial pole magnet located generally normal tothe planar surface of the housing and communicating with the ball seatthrough the aperture, a ball of magnetic electrically conductivematerial seated on the ball seat, the flux of the magnet holding theball against movement radially of the ball seat along the planarsurface, an annular series of flexible spring fingers of electricallyconductive material cantilevered on the sidewall and overlying theplanar surface, the fingers extending generally radially of the ballseat and at predetermined angles to the planar surface, the distalportions of the fingers terminating radially outwardly of the ball seatand being spaced from the planar surface a distance greater than the ODof the ball, an intermediate portion of each finger being spaced fromthe planar surface a distance generally equal to the OD of the ball,means on the planar surface providing an electrically conductive areaunder the intermediate portion of each finger, the conductive area andthe fingers being adapted to connect a source of power and a mechanismto be actuated by the sensor, an aCceleration pulse of predeterminedamplitude and time overcoming the flux of the magnet and moving the ballradially of the ball seat along the planar surface, the ball movingunderneath the distal portion of at least one finger and into wipingengagement with the conductive area and the intermediate portion of theone finger to connect the source of power and the mechanism to beactuated and to flex the one finger about the proximal portion thereof,the flexing of the one finger providing a resilient biasing force on theball directed generally radially of the ball seat and returning the ballalong the planar surface toward the ball seat upon reduction of theacceleration impulse, and means on the end wall projecting between thedistal portions of the fingers and overlying the ball seat to limitmovement of the ball laterally of the ball seat.